This invention relates to an improved process for preparing 6-hydroxyethyl-2-substituted thio-penem-3-carboxylates (referred to herein as penems). Penems are a recent addition to the family of synthetic beta-lactams and possess potent antibacterial activity.
Multistep processes for producing penems using a silver containing intermediate are disclosed in U.S. Pat. No. 4,443,393 and in our copending U.S. patent application Ser. No. 445,295, filed Nov. 29, 1982, now U.S. Pat. No. 4,530,793. These processes result in high yields, however, they are not economical since they require the use of an expensive silver containing reagent.
The process of this invention eliminates the need for the silver containing reagent while still resulting in high yields. Furthermore, in the process of this invention the compounds produced are essentially one isomeric form which results from the particular isomeric form of the azetidinone intermediate.